When we talk about evangelicals, who are we really talking about? Let's take a step back here with NPR political reporter Danielle Kurtzleben. She's been digging into the term and the numbers. Danielle, welcome to the studio.

DANIELLE KURTZLEBEN, BYLINE: Thank you.

CORNISH: So first, who are evangelicals?

KURTZLEBEN: Well, to be clear, very often when people talk about evangelical voters in a political context and especially in the context of Republicanism, people are talking about white evangelicals. White evangelicals a majority of the time tend to vote Republican, whereas black evangelicals and black Protestants as a whole, for example - they tend to vote overwhelmingly Democratic. So in these political discussions, the word evangelical has become a shorthand for white evangelical.

So as to how many there are, it depends on how you measure it. Most political polls will simply ask, do you consider yourself an evangelical? When you measure it that way, you get about 35 percent of the adult population that says yes. However, there are other ways to measure it. You can measure it by belief system. You can measure it by denomination. And depending on how you do that, you can get anywhere from 6 percent to 35 percent of the population.

CORNISH: So let's go back to white evangelicals for a minute. How important have they been to the Republican Party?

KURTZLEBEN: They've been very important. They're the largest religious group by a pretty long shot among Republicans and Republican-leaning voters. They beat out, for example, mainline Protestants and Catholics. And they're dependably Republican. They've been big supporters of George W. Bush, John McCain and Mitt Romney in the last three presidential elections, supporting them all by 75 to 80 percent in those races.

CORNISH: So how's Donald Trump been doing with this group?

KURTZLEBEN: Well, he's had the support of around two thirds of evangelicals pretty consistently across several polls throughout this race. So he may be underperforming some of those prior Republican nominees by a little bit.

CORNISH: Now, those polls I assume were before the recent news of the "Access Hollywood" tape of Trump's crude comments about women before that went public.

KURTZLEBEN: Right.

CORNISH: What do we know now about that evangelical support?

KURTZLEBEN: Well, we see some anecdotal evidence of what's going on. We saw an editorial come out of a popular Christian magazine, Christianity Today, and it definitely did not endorse Hillary Clinton. But it had some very harsh words for Donald Trump. It called him an idolater and, quote, "the very embodiment of what the Bible calls a fool." So we see exactly where they stand.

However, there are some leaders of the religious right who are still standing behind him - for example, megachurch Pastor Robert Jeffress and the Faith and Family Coalition founder Ralph Reed. So really we're seeing a bit of a divide. But as far as numbers, regular people who just go to church every Sunday - we really don't know yet. There have been a couple of polls, but they've been a little bit inconsistent.